The present invention relates to a measuring apparatus comprising a Peltier-Seebeck detector and particularly but not exclusively relates to a light power measuring apparatus.
A Peltier-Seebeck detector is commonly a planar detector with two electrical connections. When electrical voltage is passed through the detector, one side of the detector heats and the other side cools.
Conversely if one side of a Peltier-Seebeck detector is heated compared to the other, the detector is capable of producing an electrical voltage whose magnitude is approximately proportional to the temperature difference between the two sides of the detector.
This latter technique has been proposed in a measuring detector for measuring the power of a light source such as a laser for example. If light energy is applied to an exposed side of the detector, a significant proportion of that energy is absorbed causing the exposed side to be warmed relative to the unexposed side. This generates an output voltage which is proportional to the temperature difference between the two sides of the detector.
However, the temperature difference produced by relatively low power light sources can be relatively small, and the apparatus is therefore sensitive to ambient temperature changes in the environment in which the apparatus is used. This produces an output error voltage related to the change in ambient temperature across the two sides of the Peltier-Seebeck detector. This makes it difficult to achieve a stable, zero, initial detector state from which an accurate measurement of light power can be made.